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  <div class="section" id="module-linecache">
<span id="linecache-random-access-to-text-lines"></span><h1><a class="reference internal" href="#module-linecache" title="linecache: Provides random access to individual lines from text files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">linecache</span></code></a> --- 随机读写文本行<a class="headerlink" href="#module-linecache" title="永久链接至标题">¶</a></h1>
<p><strong>源代码:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/linecache.py">Lib/linecache.py</a></p>
<hr class="docutils" />
<p><a class="reference internal" href="#module-linecache" title="linecache: Provides random access to individual lines from text files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">linecache</span></code></a> 模块允许从一个 Python 源文件中获取任意的行，并会尝试使用缓存进行内部优化，常应用于从单个文件读取多行的场合。 此模块被 <a class="reference internal" href="traceback.html#module-traceback" title="traceback: Print or retrieve a stack traceback."><code class="xref py py-mod docutils literal notranslate"><span class="pre">traceback</span></code></a> 模块用来提取源码行以便包含在格式化的回溯中。</p>
<p><a class="reference internal" href="tokenize.html#tokenize.open" title="tokenize.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">tokenize.open()</span></code></a> 函数被用于打开文件。 此函数使用 <a class="reference internal" href="tokenize.html#tokenize.detect_encoding" title="tokenize.detect_encoding"><code class="xref py py-func docutils literal notranslate"><span class="pre">tokenize.detect_encoding()</span></code></a> 来获取文件的编码格式；如果未指明编码格式，则默认编码为 UTF-8。</p>
<p><a class="reference internal" href="#module-linecache" title="linecache: Provides random access to individual lines from text files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">linecache</span></code></a> 模块定义了下列函数：</p>
<dl class="function">
<dt id="linecache.getline">
<code class="sig-prename descclassname">linecache.</code><code class="sig-name descname">getline</code><span class="sig-paren">(</span><em class="sig-param">filename</em>, <em class="sig-param">lineno</em>, <em class="sig-param">module_globals=None</em><span class="sig-paren">)</span><a class="headerlink" href="#linecache.getline" title="永久链接至目标">¶</a></dt>
<dd><p>从名为 <em>filename</em> 的文件中获取 <em>lineno</em> 行，此函数绝不会引发异常 --- 出现错误时它将返回 <code class="docutils literal notranslate"><span class="pre">''</span></code> (所有找到的行都将包含换行符作为结束)。</p>
<p id="index-0">如果名为 <em>filename</em> 的文件未找到，该函数将在模块搜索路径 <code class="docutils literal notranslate"><span class="pre">sys.path</span></code> 中查找它，在此之前会先在 <em>module_globals</em> 中检查 <span class="target" id="index-3"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> <code class="docutils literal notranslate"><span class="pre">__loader__</span></code>，以涵盖模块是从 zip 文件或其他非文件系统导入源导入的情况。</p>
</dd></dl>

<dl class="function">
<dt id="linecache.clearcache">
<code class="sig-prename descclassname">linecache.</code><code class="sig-name descname">clearcache</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#linecache.clearcache" title="永久链接至目标">¶</a></dt>
<dd><p>清空缓存。 如果你不再需要之前使用 <a class="reference internal" href="#linecache.getline" title="linecache.getline"><code class="xref py py-func docutils literal notranslate"><span class="pre">getline()</span></code></a> 从文件读取的行即可使用此函数。</p>
</dd></dl>

<dl class="function">
<dt id="linecache.checkcache">
<code class="sig-prename descclassname">linecache.</code><code class="sig-name descname">checkcache</code><span class="sig-paren">(</span><em class="sig-param">filename=None</em><span class="sig-paren">)</span><a class="headerlink" href="#linecache.checkcache" title="永久链接至目标">¶</a></dt>
<dd><p>检查缓存有效性。 如果缓存中的文件在磁盘上发生了改变，而你需要更新后的版本即可使用此函数。 如果省略了 <em>filename</em>，它会检查缓存中的所有条目。</p>
</dd></dl>

<dl class="function">
<dt id="linecache.lazycache">
<code class="sig-prename descclassname">linecache.</code><code class="sig-name descname">lazycache</code><span class="sig-paren">(</span><em class="sig-param">filename</em>, <em class="sig-param">module_globals</em><span class="sig-paren">)</span><a class="headerlink" href="#linecache.lazycache" title="永久链接至目标">¶</a></dt>
<dd><p>捕获有关某个非基于文件的模块的足够细节信息，以允许稍后再通过 <a class="reference internal" href="#linecache.getline" title="linecache.getline"><code class="xref py py-func docutils literal notranslate"><span class="pre">getline()</span></code></a> 来获取其中的行，即使当稍后调用时 <em>module_globals</em> 为 <code class="docutils literal notranslate"><span class="pre">None</span></code>。 这可以避免在实际需要读取行之前执行 I/O，也不必始终保持模块全局变量。</p>
<div class="versionadded">
<p><span class="versionmodified added">3.5 新版功能.</span></p>
</div>
</dd></dl>

<p>示例:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">linecache</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">linecache</span><span class="o">.</span><span class="n">getline</span><span class="p">(</span><span class="n">linecache</span><span class="o">.</span><span class="vm">__file__</span><span class="p">,</span> <span class="mi">8</span><span class="p">)</span>
<span class="go">&#39;import sys\n&#39;</span>
</pre></div>
</div>
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